Schlenk tubes frit filtration

E. Separations. The basic filtration operation has been previously illustrated. Low-temperature filtrations for the collection of thermally sensitive compounds or products which arc soluble al higher temperatures may be performed with an H-type Schlenk tube. Fig. 1.30, in a large low-temperature bath. The jacketed, fritted funnel illustrated in Fig. 1.25 also permits low-temperature filtration. 

Filtration. One of the most convenient aspects of the cannula techniques is that filtration does not require the use of fritted glass equipment. Small scale filtrations are simply carried out by transferring the liquid to be filtered from one Schlenk tube to another through a filter stick as shown in Figure 5. When the filtration is complete the filter paper is discarded, and the cannula washed with acetone to prepare it for the next filtration. The advantages of filter stick filtration over filtration through fritted glass apparatus maybe summarized as follows ... 

The reaction can be conducted with standard Schlenk techniques. All manipulations must be carried out under purified nitrogen, and all solvents must be distilled over drying agents and saturated with nitrogen prior to use. In a 250-mL Schlenk tube, 640 mg (1 mmol) of Ru3(CO),2 [Alfa] and 160 mg (4 mmol) of Na[BH4] are dissolved in 100 mL of tetrahydrofuran. The solution, which turns dark red, is stirred at 25° for 30 min. The reaction mixture is filtered through a 2-cm layer of filter pulp, using a 250-mL Schlenk frit, and the filtrate is evaporated to dryness. The residue is dissolved in methanol (30 mL), and after addition of Et4NBr (250 mg, 1.2 mmol) in methanol (10 mL), the solution is concentrated to 10 mL. The product is allowed to crystallize at room temperature for 6 hr then the solution is cooled to — 78°. After 15 hr, the crystalline... 

The complete reaction was performed under Schlenk conditions. Dry diethyl ether (250 mL) was placed in 500 mL Schlenk three-necked flask equipped with a dropping funnel and reflux condenser. The dropping funnel was charged with a mixture of 31.9 g (389 mmol, 2 equiv) 1-methylimidazole and 38.9 g (389 mmol, 2 equiv) 2-methylpent-4-en-2-ol in 50 mL diethyl ether. One quarter of the prepared mixture was added to the diethyl ether. The 19.6 g (194 mmol, 1 equiv) dichlorosilane condensed into a Schlenk tube at -78°C were allowed to slowly diffuse into the stirred reaction mixture at —78°C. Meanwhile the residual mixture from the dropping funnel was slowly added to the reaction mixture which is then stirred for a further 10 h at room temperature. The resulting methylimidazole hydrochloride was removed by filtration through a Schlenk frit and the solvent was evaporated imder reduced pressure (200 mbar). After fractionated condensation in vacuo (0.3 mbar, 60°C) 35.7 g (156 mmol, 81%) bis((2-methylpent-4-en-2-yl)oxy)silane were obtained as a colorless liquid. 

The oil is dissolved m 500 mL of diethyl ether under a nitrogen atmosphere, cooled to -78°C in a dry ice-acetone bath and 18 g (0.11 mol) of tetrafluoroboric acid-diethyl ether complex is added dropwise by syringe over a 30-min period, while the bath temperature is maintained at -780C. The solution is allowed to warm to room temperature, and the powdery yellow solid is isolated by filtration through a 250-mL, coarse-frit, Schlenk filter tube. The product is washed several times with fresh ether and dried under a stream of nitrogen and then under reduced pressure (oil pump). The yield of salt 3 is 31-39.1 g (60-75%). The product may be used without further purification (Note 17) and may be stored under nitrogen at 0°C for several weeks with no observable decomposition (Note 18). 

---